1. Field of the Invention
This invention relates to a method and apparatus for the production of color separations for textile, decoration or packaging printing and the like in which a colored pattern model is trichromatically scanned point-by-point and line-by-line for the generation of color signals and is then again recorded.
2. Description of the Prior Art
Whereas the color application on a printing medium in multi-color mixed printing occurs by means of the superimposed printing of different components of the separation colors magenta, cyan and yellow, in textile, decoration and packaging printing and the like, each color to be printed is mixed before the printing process, in most use cases, and are then separately transferred to the printing medium.
The pattern models for the above-mentioned types of printing, for example, exhibit color areas residing separately next to one another of different coloration with a homogeneous color distribution within the color areas (full tone color area). In this case, line color separations are produced for the individual pattern colors with the assistance of a color scanner, which line color separations supply specific information concerning the local distribution of the pattern colors in the pattern model.
Other pattern models with color areas likewise residing separately next to one another of different coloration exhibit an analog graduated color distribution, i.e., differing color saturation and/or brightness within the individual color areas graduated tone color areas). However, pattern models also occur which are designed vignetting and two-dimensional, or which exhibit a multitude of vignetting colors randomly verging into one another. In these cases, analog graduated color separations like continuous tone or half-tone color separations must be produced for the individual pattern colors, which color separations supply specific information concerning both the local distribution of the pattern colors in the pattern model and specific information concerning the amount of color.
A color recognition circuit and its use in a color scanner for recording color separations for the above types of printing is already known from the British Pat. No. 1,522,950, which is fully incorporated herein by this reference.
In such a color scanner, three primary measured color value signals are obtained by means of point-by-point and line-by-line optoelectronic pattern scanning, which measured color value signals represent the color components red, green and blue of the scanned image points. The color recognition circuit charged with the measured color value signals selects the individual pattern colors and generates specific output signals which modulate the brightness of recording lamps, as recording organs, as color separation signals. The recording lamps expose a recording medium in the form of films point-by-point and line-by-line, which films, after development, represent the desired, screened or unscreened color separations for the production of the printing forms.
In the mentioned color recognition circuit, the individual color recognition areas into which the entire color space is divided are respectively marked by means of the position of a barycentric color and by means of shape, extent and orientation in the color space. The color separation signal generated for each pattern color is a function of the distance of a color location from the color location of the selected barycentric color, whereby the color separation signal has a maximum value at the barycentric color, decreases towards the limits of the color recognition area and becomes zero at the specific limits. The respective color separation signals supplies specific information concerning the color saturation and/or brightness in a graduated tone color area and is proportional to the density in the appertaining color separation to be recorded.
The known arrangement has the disadvantage that the color recognition areas which can be set in the color recognition circuit specified cannot be optimally matched in terms of form and size to the spatial color regions given by the vignetting colors of the pattern model. For this reason, color errors in the production of the color separations cannot be entirely avoided. It is further disadvantageous that whether or not the barycentric color within a color area of the pattern model was properly selected or not can only be determined on the basis of a recorded color separation and that the most favorable barycentric color can often only be found by means of the exposure of a plurality of color separation proofs.